The natural history and immune response of women with HSV infections were studied. Most virus isolates from 50 pregnant women were serotyped as HSV-II or very similar to HSV-II. None of the isolates typed as HSV-I. Antibody to HSV-II as measured by neutralization or by indirect hemadsorption tended to rise early but did not correspond with clinical symptoms while cytotoxic antibody arose later and tended to correspond better with clinical symptoms.